Cladistic, phenetic and biogeographical analysis of the flightless dung beetle genus, Gyronotus van Lansberge (Scarabaeidae : Scarabaeinae), in threatened eastern Afrotropical forests

By virtue of their low vagility, flightless insects are useful indicators o f biogeographical history. Relationships of the flightless dung beetle genu s, Gyronotus, are of particular interest due to its Gondwanaland ancestry, distinctive relict distribution along the south-eastern seaboard of Africa, and its restriction to forests which are seriously threatened by exploitat ion. Because of the limited number of diagnostic morphological characters, it was necessary to code morphometric data in order to conduct distance and cladistic parsimony analysis of interspecific relationships in Gyronotus. There was a good correlation between relationships indicated by the dendrog rams/cladograms and those determined by an examination of aedeagus characte r states both of which indicate a disjunction between south and east Africa n species and a broad separation between northern and southern South Africa n species. Comparison of the bilaterally asymmetrical aedeagi of Gyronotus with the symmetrical aedeagi of the sister genus, Anachalcos Hope, suggests geographical polarization of character states from greater plesiomorphy in east African Gyronotus to greater apomorphy in South African species, part icularly in the southernmost element in which the aedeagus shows extreme as ymmetry. Furthermore, body shape follows a similar geographical gradient in that the three Gyronotus species of tropical east Africa are significantly more elongate than the three ovoid, lowland/afromontane species of South A frica. An examination of historical factors suggests that this spatially-re stricted distribution is the relict of a very old tropical lowland pattern. In extant taxa, the phylogenetic polarization is towards one of five main centres of afrotropical forest biodiversity in the geologically old Eastern Arc and the adjoining lowland forest (Swahili centre of endemism). Survivo rs from old lineages may be one reason for such centres. of high biodiversi ty.